A head-up display device is capable of displaying information in a manner overlapped with the background at the end of the line of sight. Incorporating such a head-up display device, for example, in an automobile allows for projecting, at the end of the line of sight such as a windshield, an image including information such as speed obtained by instruments in the vehicle while driving the automobile, which facilitates driving without changing the eyesight and may lead to accident prevention.
There is known a type of head-up display device including, for example, a combiner adhered inside a windshield, with the vertical cross section of the combiner being wedge-shaped and made relatively thinner at the lower part where a visual display device is located so as to prevent formation of a double image (Patent Literature1).
There is known a type of head-up display device including, for example, a combiner provided in an upright manner on the inside of a windshield in a manner separated from the windshield, with the radius of curvature being smaller at the observer's side (Patent Literature2).
However, the combiner according to Patent Literatures 1 and 2, has not sufficiently taken into consideration of the thickness of the lateral section and, even when the double image of the image in the vertical direction at the central part with regard to the lateral direction is dissolved, the double image in the periphery with regard to the lateral direction is not sufficiently dissolved, thereby resulting in degradation of the image quality as a whole. Particularly, significant degradation of the image quality occurs in the case with a wide viewing angle and a wide eye box.